The present invention relates to a magnetron with a magnet assembly suitable for sputtering or reactive sputtering of materials from a cathode target onto a substrate as well as a method of operating the magnetron.
There have been many attempts to improve the erosion profile of sputtering magnetron targets and/or deposition uniformity onto a substrate by moving a magnet array relative to the target. For example, a rectangular planar magnetron with a moveable magnet assembly is known from U.S. Pat. No. 4,444,643 in which the magnetic assembly is translated laterally and parallel to the major axis of the target, DE-A-27 07 144 proposes a magnet assembly which is swept over a rectangular target along a linear path, U.S. Pat. No. 4,714,536 proposes that the magnet assembly is moved with a non-repetitive epicycloidal motion combined with a translational motion over the target, i.e. the magnet array performs a non-repetitive small epicycloidal motion distributed over the area of the target, U.S. Pat. No. 5,188,717 explains that even erosion of the target can be obtained when the dwell time of the magnetic flux remains equal over each unit area of the target and proposes a specific shape to the magnet assembly, U.S. Pat. No. 5,382,344 describes a magnet assembly which produces electron paths in a plurality of race-tracks, the race-tracks are moved linearly and perpendicularly to the longest axis of the target with an oscillatory motion, EP-A-416 241 describes a magnet array which may be moved in an oscillating motion limited by the cathode tray, the motion being produced by a pin on a rotating cam, the pin being journalled in the base of the magnet array, U.S. Pat. No. 5,328,585 discloses a linear planar magnetron sputtering apparatus with a reciprocating magnet array, the reciprocating motion can be simultaneously lateral and longitudinal with respect to the cathode target, and U.S. Pat. No. 5,833,815 proposes reciprocating motions parallel to the substrate moving direction and at an angle thereto. A suitable motion of the magnet array may be determined by trial and error, by simulation, or simply by a good engineering guess. Whichever method is used actual target erosion may still show localised areas of preferential erosion where the magnetic flux resides for longer time per unit area than in other areas (dwell times) or areas where less of the target is eroded due to the fact that the magnetic flux has a localised shorter dwell time.
U.S. Pat. No. 5,417,833 discusses previous attempts to achieve uniform target erosion and points out that minor changes in the shape of the magnet array can lead to dramatic changes in erosion profiles. It is pointed out that it is difficult to marry actual magnetron results with strict mathematical analysis, the interaction of plasma with magnetic and electric fields not being a trivial problem. To improve the operation of the magnetron it is proposed to include not only a rotating magnet array but also a stationary electromagnet. A point on the racetrack generated by the magnetic field from the rotating magnet array always stays at the same distance from the electromagnet. Further, the teachings of U.S. Pat. No. 5,417,833 are related to a very special magnet array geometry and cannot be extended easily to other geometries and movements. The reason is that an electromagnet only produces a magnetic field in specific directions and/or at specific periodic times. However, a moving magnet array exerts at any one position on a target a magnetic field whose vector varies with time. Hence, it is necessary to compensate at any one position of the target for an imposed magnetic field having a varying vector, which generally will require a compensating field at this target position whose vector also changes. This is not easy with an electromagnet and hence, it is generally not possible to compensate for moving magnetic fields with changing magnetic field vector with an electromagnet particularly when the geometry of the magnet array and/or the motion of the magnet array is complex.
It is the object of the present invention to provide a sputtering magnetron with a moveable magnet array which is simple in construction, reliable and provides uniform target erosion.
Further, it is an object of the present invention to provide a simple erosion profile compensation device particularly for a planar magnetron.
It is a further object of the present invention to provide a moving magnet assembly which provides a high utilisation of the material of the target at least in a central region thereof.
It is still a further object of the invention to provide a method of operating a magnetron with moving magnet array so as to provide uniform target erosion.
The present invention provides a magnetron including a target for sputtering onto a substrate, the magnetron comprising: a magnetic field generator for generating a closed loop magnetic field adapted to generate a plasma race-track above the target; a driving device for establishing relative substantially translational movement between the race-track and the target; and one or more pieces of ferromagnetic material fixed with respect to the target and adapted to influence the magnetic field generated by the magnetic field generator at least during part of the relative substantially translational movement, the distance between any point on the race track and the momentarily closest part of the one or more pieces of ferromagnetic material varying according to the relative substantially translational movement of the race-track and the target. The one or more pieces of ferromagnetic material are preferably mounted close to the magnetic field generator. The movement produced by the establishing means may be repetitive re-entrant or repetitive non-re-entrant. The one or more pieces of ferromagnetic may be placed, according to one embodiment, at positions located so as to reduce excessive local erosion of the target. Alternatively or additionally, according to another embodiment of the present invention, the pieces may be placed at positions which reduce the rate of material sputtered from outside the target.
In the magnetron according to the present invention described above the magnetic field generator may be an array of permanent magnets or an electromagnet or electromagnets which move to create the race-track movement defined above. Alternatively, an array of stationary electromagnets may be used and the movement of the race-track may be produced by varying the magnitude and relative phases of the currents among the electromagnets of the array. The one or more pole pieces are preferably mounted close to the magnet generating means. The movement produced by the establishing means may be repetitive re-entrant or repetitive non-re-entrant.
The present invention also includes a method of operating a magnetron having a target and a magnetic field generator, comprising the steps of: generating a closed loop magnetic field using the magnetic field generator; generating a plasma race-track above the target using the generated closed loop magnetic field; moving the plasma race-track relative to the target; and locating one or more pieces of ferromagnetic material at positions stationary with respect to the target so that the magnetic field of the magnetic field generator is influenced at least during a part of the relative translational movement, the distance between any point on the race track and the momentarily closest part of the one or more pieces of ferromagnetic material varying according to the relative movement of the race-track and the target. The one or more pole pieces are preferably mounted close to the magnetic field generator. The movement of the race-track may be repetitive re-entrant or repetitive non-re-entrant. The one or more pole pieces may be placed, according to one embodiment, at positions located so as to reduce excessive local erosion of the target. Alternatively or additionally, and according to another embodiment of the present invention, the pole pieces may be placed at positions which reduce the amount of material sputtered from outside the target.
The present invention may also provide a method of improving target erosion of a sputtering magnetron, the sputtering magnetron having a race-track generator which generates a race-track which moves relative to a target, comprising the steps of: simulating the operation of the magnetron on a processing engine; determining from the simulation local areas of the target with excessive or reduced target erosion; simulating the effect of one or more pieces of ferromagnetic material fixed with respect to the target at locations neighbouring the local excessive or reduced erosion areas in the target; selecting a shape, thickness and material for the one or more pieces based on the results of the simulation in order to reduce the degree of excessive or reduced erosion of the local areas of the target. The processing engine may be a suitable computer such as a Personal Computer or a workstation.
The present invention also includes a method of improving target erosion of a sputtering magnetron, the sputtering magnetron having a race-track generator which generates a plasma race-track which moves relative to a target, comprising the steps of: inputting a description of the magnetron at a near location; transmitting the description to a remote processing engine running a magnetron simulation program; and receiving at the near location descriptions of one or more pieces of ferromagnetic material as well as locations for the fixing of these pieces stationary with respect to the target. The processing engine may be a suitable computer such as a Personal Computer or a workstation. Transmission between the near and far locations may be by suitable telecommunications networks, e.g. via the Internet. The processing engine may be connected to the telecommunications network by suitable modems. The simulation program may determine local areas of the target with increased target erosion, simulate the effect of one or more pole pieces of magnetically permeable material fixed with respect to the target at locations neighbouring the increased erosion areas of the target and select a shape, thickness and material for the one or more pole pieces based on the results of the simulation in order to reduce the depth of increased erosion areas of the target.
The present invention may provide the advantages of good utilisation of target materials while still providing a mechanically simple and reliable magnet assembly and drive.
The dependent claims define further embodiments of the present invention. The present invention, its advantages and embodiments will now be described with reference to the following drawings.